AGE-RELATED CHANGES IN METABOLIC PARAMETERS OF NON-HUMAN PRIMATES





X.T. Tigno, I.K. Selaru, G. Gerzanich and B.C. Hansen

Obesity and Diabetes Research Center, Department of Physiology, School of Medicine, University of Maryland at Baltimore, 10 South Pine St., Baltimore, MD 21201



Type 2 diabetes is closely associated with aging, making it difficult to distinguish which of the symptoms attributed to type 2 diabetes are actually manifestations of the aging process. A colony of rhesus monkeys with ages ranging from 2 to 32 years, some of whom spontaneously develop obesity and diabetes, was followed up for a period of 10 or more years. Routine clinical chemistry and hematology, intravenous and oral glucose tolerance testing, and the euglycemic, hyperinsulinemic clamp procedure, were performed periodically to assess metabolic status. Comparing values obtained by averaging over two-year intervals, no age- related changes in Fasting Plasma Glucose (FPG) and 2-hours post-OGTT glucose could be demonstrated among non-diabetic (N) monkeys. On the other hand, mean values of FPG as well as 2-hours post OGTT glucose were already significantly elevated over the normal group by age 14 for monkeys who eventually developed diabetes (DM). An age - related decline in Fasting Plasma Insulin levels, the acute insulin response (AIR), the two-hour post- OGTT- insulin levels, and the glucose disappearance rate post- IVGTT (Kg) was evident in both the N and DM groups. Insulin sensitivity (M rate), however, did not appear to change. Circulating triglyceride levels did not change significantly with age in the non-diabetic group, but was significantly higher among the diabetics from age 14. Similarly, no age- related elevation in total cholesterol, LDL- cholesterol, VLDL-cholesterol, and VLDL- Triglyceride levels could be detected among the non-diabetics; however, HDL-cholesterol levels appeared to be higher among the younger subjects ( age < 10 years) than among the elderly. Longitudinal assessment of the clinical status of this colony of non-human primates makes it possible to differentiate which changes in the physiologic variables may be attributable to diseases of aging, including the metabolic syndrome, and which are normal correlates of the aging process.




Key words: obesity, diabetes, aging, metabolic syndrome,lipids







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